1. Field of the Invention
The present invention generally relates to a gas exhausting apparatus of wet electrophotographic image forming device, and more particularly, it relates to a gas exhausting apparatus of wet electrophotographic image forming device which is capable of oxidizing and thermally decomposing impurities such as combustible hydrocarbon (CmH2n) etc. included in a gas generated when a toner image transferred on a sheet of paper is fused by heat and pressure, and then exhausting the gas.
2. Description of the Related Art
Generally, an electrophotographic image forming device such as color laser printer uses a liquid toner including a carrier solution of a hydrocarbon system such as, for example, a compound of C10H22, C11H24, C12H26 and C13H28, a pigment, etc., as a developer for printing. Almost all of the carrier solution included in such a liquid toner is withdrawn into a developer storing unit during the processes of developing a toner image onto a photosensitive body through a developing roller, and transferring the toner image formed on the photosensitive body onto a transfer belt, but a portion of the carrier solution still remains in the toner image until fusing or a fusing/transferring operation. During the fusing or the fusing/transferring operation, the toner image is fused or fixed on a sheet of paper by a pressing roller and a heating roller of a fusing unit . During this operation, the part of the carrier solution remaining in the toner image evaporates. This evaporation generates a combustible hydrocarbon gas by the heat radiated by the pressing roller and the heating roller . This gas is then exhausted to the outside.
However, the combustible hydrocarbon gas generated due to evaporation of the carrier solution is a volatile organic compound (VOC) that contaminates the surrounding environment and has an unpleasant smell. Accordingly, the combustible hydrocarbon gas is preferably removed from the air before it is exhausted to the outside of the printer.
As mechanisms to remove such a combustible hydrocarbon gas, there are known a filtering method to physically filter a gas ingredient, a direct combustion method that oxidizes and burns the gas ingredient at a temperature (600–800° C.) above a combustion point of the gas ingredient, a catalyst oxidation method that oxidation decomposes or thermally decomposes the gas ingredient into a water vapor and a carbon dioxide by using a catalyst with chemically burning or oxidizing it at a relatively low temperature (150–400° C.).
FIG. 1 shows a gas exhausting apparatus 10 inhaling air of high temperature including a hydrocarbon gas generated due to evaporation of carrier solution in a printer 1 during a printing operation including fusing or fusing/transferring, removing the hydrocarbon gas from the air of high temperature by the filtering method, and then exhausting the air to the outside of the printer 1.
The gas exhausting apparatus 10 is provided with an exhaust fan 13 inhaling the air in the vicinity of a fusing unit 11 of the printer 1 and exhausting the air to the outside of the printer 1, and a filter 12 disposed between the exhaust fan 13 and the outside of the printer 1 to filter impurities including the hydrocarbon gas in the air. The filter 12 is composed of a dust collecting part 12a collecting dust, etc., and an active charcoal 12b absorbing and removing the hydrocarbon gas.
Accordingly, as the air inhaled from the inside of the printer 1 by the exhaust fan 13 passes through the filter 12, the hydrocarbon gas therein is absorbed and collected in the active charcoal 12b. It is then exhausted to the outside of the printer 1.
However, the gas exhausting apparatus 10 constructed as above has a disadvantage in that the filter 12 should be frequently exchanged in order to maintain its filtering performance, since the active charcoal 12b cannot absorb hydrocarbon gas after it is saturated by absorbing large amounts of the hydrocarbon gas over time.
Also, the gas exhausting apparatus 10 presents a safety concern in that a user can be directly exposed to the high temperature air and get burned, since the high temperature air is exhausted to the outside of the printer 1 directly after passing through the filter 12.
To solve these problems, as shown in FIG. 2, there has been proposed a gas exhausting apparatus 10′ that inhales air of high temperature including a hydrocarbon gas generated in a printer 1′, removes the hydrocarbon gas from the air of high temperature by the direct combustion method, and then exhausts the air to the outside of the printer 1′.
The gas exhausting apparatus 10′ includes an exhaust line L forming an air flow path from a fusing unit 11′ to the outside of the printer 1′, an exhaust fan 40 disposed in the middle of the exhaust line L to inhale and exhaust the air in the printer 1′, a combustor 20 heating and chemically burning or oxidizing the air discharged from the exhaust fan 40, a heat exchanger 30 cooling the air heated by the combustor 20, and a dust collecting part 33 removing a dust etc. included in the air.
The combustor 20 includes a heater 21 having a heating temperature of about 1,000–1,300° C. The heater 21 thermally decomposes the hydrocarbon gas in the air that moves along the exhaust line L, thereby to resolve it into a water vapor and a carbon dioxide, and then to exhaust it.
The heat exchanger 30 is provided with a coil tube 31 formed in a spiral shape to increase the moving time of the air, and a cooling fan 32 exchanging heat by blowing air to an outer surface of the coil tube 31 to cool the coil tube 31.
In operation, the hydrocarbon gas in the air inhaled into the combustor 20 by the exhaust fan 40 is thermally decomposed by the heater 21, cooled by the coil tube 31 and the cooling fan 32 of the heat exchanger 30, and then exhausted to the outside of the printer 1′ through the dust collecting part 33.
In the conventional gas exhausting apparatus 10′, since the hydrocarbon gas is exhausted after being thermally decomposed by the heater 21 and cooled by the coil tube 31 and the cooling fan 32, the disadvantage of frequent exchange of the filter 12 and the safety problem due to direct exhausting of the high temperature air as in the gas exhausting apparatus 10 shown in FIG. 1 are solved.
However, since the conventional gas exhausting apparatus 10′ additionally uses the cooling fan 32 and the coil tube 31 to cool the high temperature air as well as the exhaust fan 40, fabrication costs are increased, and structure is complicated, thereby making fabrication difficult.
Also, since the conventional gas exhausting apparatus 10′ uses high-priced heater 21 having the heating temperature of about 1,000–1,300° C. to resolve the hydrocarbon gas into the water vapor and the carbon dioxide by thermally decomposing it, fabrication and maintenance costs are increased.
To decrease the heating temperature of the heater 21, as shown in FIG. 3, there has been proposed a gas exhausting apparatus 10″ in which a platinum catalyst 22 is disposed around a heater 21 of a combustor 20′ to promote oxidation of a hydrocarbon gas generated by printer 1″.
However, the gas exhausting apparatus 10″ has an advantage in that it can oxidize and thermally decompose the hydrocarbon gas by maintaining a heating temperature of the heater 21 in about 250–300° C., but a problem that fabrication cost and complication in structure are increased due to additional use of a cooling fan 32 and a coil tube 31 of heat exchanger 30 is not still solved.